INS and dementia: The subgroup analysis showed that compared with the levels observed in the HCs, serum insulin levels were significantly higher in the patients with nonpsychotic dementia (25 sets of data were extracted from 17 studies; Hedges' g = 1.482, 95% CI = 0.909 to 2.056, and P = 0.000), and the same trend was observed in the plasma (13 sets of data were extracted from 9 studies; Hedges' g = 0.445, 95% CI = 0.154 to 0.736, and P = 0.003).